Co-extruded films have a number of functional requirements, which includes barrier properties against gases, such as oxygen, puncture resistance, sealability, printability, as well as retort resistance.
Moreover, packaging is becoming more and more important as a communication tool for food companies and brand owners to convey product messages to consumers. Transparency, as well as higher gloss becomes critical for a fresh, trendy, appealing product image. Co-extruded films comprise at least a skin layer and a sealing layer. Copolyamide is a known material for skin layer, also called outer layer, as it is co-extrudible with polyethylene, polypropylene as well as ethyl vinyl alcohol, and because it is high temperature resistant during sealing. However, the gloss of the copolyamide is insufficient. This results in a film with dull appearance, which is undesirable. Moreover, asymmetric films may suffer from curling behavior. Curling behavior is the phenomenon that a film deviates from planar geometry, as for example curling into a tube-like structure. This may damage the functionality or appearance of an end product, such as a lidding film on a tray. It may also disrupt a process step upon further processing the film into packaging.
Upon sterilizing or pasteurizing packages containing a packed product and a film, it may happen that the packages adhere to each other, as these packages are often treated while being stacked on top of each other. This is unwanted, as the packages then have to be peeled from each other and may even open up after the sterilizing or pasteurizing process. Packed products may include food such as vegetables, fruit, cheese, meat, as well as non-food stuffs.
It is thus an objective of the present invention to provide a co-extruded film which has better properties making it more attractive to employ in packaging, such as lidding film. This has been achieved by a co-extruded film comprising a sealing layer of a polyolefin and a skin layer, wherein the skin layer comprises a copolyamide which comprises:                At least 75 wt % monomeric units derived from caprolactam;        Between 5 to 25 wt % monomeric units derived from a diamine and terephthalic acid;wherein the weight percentage is with respect to the total weight of copolyamide in the skin layer.        
The sealing layer is a polyolefin, such as for example polyethylene, polypropylene, low density polyethylene (LDPE), linear low density polyethylene (LLDPE). Preferably, the sealing layer is a low density polyethylene. This has the advantage that the melting temperature of LDPE is relatively low, which facilitates sealing.